How did you add it in the Pb Manager in WrpEdit?
If we suppose your tower was called Tower.pbo and you found the entry \Tower in the Pb Manager and tried to use that to add the tower, it won't work.
You need to click the Add icon in the top left corner of the Pb Manager interface, navigate to where you have the Tower.pbo, i.e. Addons, and choose it from there, then the Tower will appear in the list in the Pb Manager nearer the bottom of the list and it will not have the '\' in front of its name.
Hope this helps.
Planck